Packaging and methods for reducing odors and strength loss caused by the irradiation of polyolefin-based products

ABSTRACT

The invention provides a method for reducing or eliminating the odors commonly produced by the sterilization of polyolefin-based products by gamma radiation. In addition, the invention also provides a method for minimizing the amount of fabric strength loss associated with the irradiation process and a method for actually increasing the fabric strength of a polyethylene that has been irradiated. Both the reduction in odors and the minimization of strength or increase in polyolefin strength are achieved in methods comprising the use of an oxygen scavenger. The invention further includes the use of non-gamma stabilized polyolefins. The polyolefinic product may also include an odor mask that may be used to mask any residual odor.

This application is a continuation of application Ser. No. 07/994,792,entitled "Packaging and Methods For Reducing Odors and Strength LossCaused by the Irradiation of Polyolefin-Based Products" and filed in theU.S. Patent and Trademark Office on Dec. 21, 1992, and now abandoned.

FIELD OF THE INVENTION

The invention generally concerns the use of an oxygen scavenger toreduce or eliminate the undesirable side effects associated with thegamma irradiation of polyolefin-based products.

BACKGROUND OF THE INVENTION

Various fields of use require the use of sterilized polyolefin-basedclothing, equipment and tools. For example, it is well known that theoperating environments of medical personnel, dental personnel, chemicalresearch personnel, biotech personnel, and other like areas of use allrequire the use polyolefin-based workwear products that have beensterilized prior to use.

In the past, ethylene oxide has been used to sterilize polyolefin-basedproducts such as medical fabrics that are used as surgical gowns anddrapes. However, the potentially hazardous nature and high cost ofethylene oxide sterilization have caused the medical community toconsider different sterilization methods. One effective method ofsterilization has been the use of gamma irradiation.

Although sterilization by gamma irradiation of polyolefin-based productsand equipment has been successful, there remain at least two veryundesirable side effects caused by the irradiation process. The firstundesirable side effect has been a resulting odor that is so extremethat it renders the gamma irradiated polyolefin-based productundesirable for many uses. The second undesirable side effect has been anoticeably decreased strength of the irradiated polyolefin products. Infact, the irradiation process has been known to decrease apolyolefin-based product's tear strength by as much as 65% of itsnon-irradiated tear strength.

It has been shown that the cause for the undesirable odor and the lossin fabric strength is a free radical process that occurs when thepolyolefins of the product are exposed to gamma radiation in thepresence of oxygen. In polyolefin-based products, this processessentially breaks chemical bonds that hold a polyolefin chain togetherand creates free radicals. This breaking of the polyolefin backbonecauses the polyolefin to lose strength proportional to the radiationdosage. The formed radicals are able to recombine with the oxygen in theair, producing short chain acids, oxygenated compounds, such as thatbecome trapped in the product. Butyric acid, one of the acids formed, isa primary suspect in causing the odor.

In efforts to combat these two undesirable side effects, others havetried various processes. For example, U.S. Pat. No. 3,194,668, to Scheinand Liberte teaches a process for preparing radiation-stabilizedpolyethylene products that adds an amount of 2,2'-methylene-bis-(4-ethyl-6-t-butyl phenyl) to the polyethylene prior toits being sterilized. U.S. Pat. No. 4,501,789 to Burch teaches thepretreatment of polypropylene products with rosin esters, anti-oxidantsor prodegradants to reduce the odor caused by the gamma-irradiation ofpolypropylene products. Further, U.S. Pat. Nos. 4,501,789 and 4,617,230to Shah, et al. teach the sterilization treatment of polyolefin-basedlatex non-woven fabrics with an odor inhibition agent selected fromamine-type antioxidants and hindered phenols.

Although the above-described patents have taught methods that marginallyreduce the odor associated with the gamma irradiation ofpolyolefin-based products, none has adequately reduced the odor orminimized the reduction in tear strength resulting from the irradiationtreatment. A need therefore exists for a method for minimizing oreliminating the odor that is associated with the gamma irradiation ofpolyolefin-based products. A need further exists for a method that notonly reduces the odor, but also minimizes any decrease in the strengthof the polyolefin product that is due to the gamma irradiation. Ideally,this need will be satisfied by a method that not only minimizes thepolyolefin strength loss, but in fact, actually increases the strengthof the post-irradiated polyolefin product.

It is therefore an object of the invention to provide a method forreducing both the odor and the polyolefin strength loss associated withthe gamma irradiation process.

SUMMARY OF THE INVENTION

The invention comprises a method for reducing oxygen in packaging ofpolyolefin-based products with an oxygen scavenger prior tosterilization by gamma radiation such that both the odor associated withthe irradiation of the polyolefin-based product is eliminated or reducedand the post-irradiation strength of the polyolefin-based product iseither only minimally decreased or actually increased.

The polyolefin-based products of the present invention may be eithercopolymers, such as copolymers of propylene and ethylene, orhomopolymers consisting of, for example, 100% polypropylene, or blendswith other polymers, both thermoplastic and non-thermoplastic.

The oxygen scavengers of the present invention include iron compounds,copper compounds, vitamin C based compounds, and other like compounds.The product, i.e., fabrics, etc., is generally of the polyolefin family,in particular, polypropylene, polyethylene, or copolymers thereof, andincluding blends with these polyolefins.

The invention also comprises carrier means such as a cellulose-basedcard that carries or has been treated with an oxygen scavenger and amethod for using the treated card as a means for reducing or eliminatingthe odor and the post-irradiation strength loss of the irradiatedpolyolefin-based products. In this method, the card may be packaged withthe polyolefin-based product inside the package to be sterilized. Whenthe polyolefin-based product is in the form of a polyolefin-based fabrictype material, such as a surgical gown, the card may additionallyfunction as a tie card that allows the user to aseptically tie the gown.

The invention further includes an odor mask and an odor scavenger thatmay be used in conjunction with the oxygen scavenger.

BRIEF DESCRIPTION OF THE DRAWING

The Figure illustrates a package in accordance with the inventioncontaining an oxygen scavenger.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The inventors of the present invention have discovered that theintroduction of an oxygen scavenger inside the packaging of apolyolefin-based product significantly reduces or eliminates theassociated odor, and either minimizes the reduction in strength, oractually increases the strength of the polyolefin-based product afterthe package and its contents have been sterilized. The oxygen scavengerremoves the oxygen that is present in the packaging prior to gammairradiation. When the product is irradiated, some of the bonds in thepolyolefin chains are broken and combine with available oxygen, whichleads to more chain scission, thereby weakening the product. With thepresent method, the product is irradiated, causing the breakage of someof the polyolefin chains, but there is little or no oxygen to combinewith the bonding sites in the broken polyolefin chains. The availablebonding sites in the polyolefin chains are therefore free to recombinewith one another instead of with oxygen in the package such that themajority of the strength of the irradiated product is maintained. In thecase of polyethylene the strength of the irradiated polyolefin productmay actually be greater than the pre-radiation strength of the product.It is believed that the strength increase is attributable to therecombination of the original chains plus cross-linking with otherparallel polyolefin chains. In the presence of oxygen, the amount ofcross-linking phenomenon which occurs is reduced due to a much fasterreaction with oxygen. The minimization of the potential for theformation of oxygenated compounds, such as short-chain organic acids,with consequent reduction or elimination of odors associated therewith,also comprises a feature of the present invention, as do products whichexhibit such characteristics.

In addition, the oxygen scavenger also functions to reduce or eliminatethe odor associated with the irradiated product as there is minimaloxygen present to combine with the radicals produced by the irradiation.The present invention is primarily directed to a polyolefin-basedproduct, such as a nonwoven fabric. The fabrics of the present inventionare generally selected from the polyolefin family. More specifically,the polyolefins may either be homopolymers or copolymers. The preferredhomopolymer is polypropylene, and the preferred copolymer is apropylene/ethylene copolymer. The amount of propylene in the copolymermay range from 90% to 100%, and the amount of ethylene in the copolymermay range from 0 to 10%. It should be appreciated that as the amount ofethylene is increased, the flexibility of the fabric being produced willalso be increased. The inventors have therefore determined that thepreferred copolymer is 97% propylene and 3% ethylene.

The process and method for making the polyolefin-based fabrics are wellknown in the art. See for example U.S. Pat. Nos. 4,041,203 and4,340,563, herein incorporated by reference.

The weight of the produced fabric, represented in ounces per square yardis normally determined by the intended use thereof. For example, if thefabric is to be used as a vehicle cover, the weight of the fabric shouldgenerally be in the range of 7.20 ounces per square yard. If the fabricis to be used as a diaper liner, the weight of the fabric shouldgenerally be in the range from 0.3 ounces per square yard to 0.8 ouncesper square yard. For surgical gowns, the fabric weight should range from0.8 ounces per square yard to 3.0 ounces per square yard.

The preferred polyolefin-based fabric of the present invention is "SMS"which may be obtained from the Kimberly-Clark Corporation. SMS is a"spun-bond, melt-blown, spun-bond" polyolefin-based laminate fabric inwhich the "spun-bond" layers represent continuous larger polyolefinfibers that impart strength and a "melt-blown" layer that is comprisedof smaller polyolefin fibers that act as a barrier. In combinationtherefore, the SMS fabric is a resilient and resistant fabric that isideal for medical fabrics such as surgical gowns. SMS is alsoparticularly useful, for example, as a surgical gown because it has goodliquid and particle barrier properties, high breathability, low lint,and is resistant to ignition.

A gamma stabilizer, such as a benzoate ester, may be incorporated intothe polyolefin prior to polyolefin extrusion. In the past, it hasgenerally been believed that a gamma stabilizer must be added to thepolyolefin in order to stabilize the polyolefin for the gammairradiation process. This step was taken in an effort to minimizepolyolefin strength loss and decrease odors. However, the inventors ofthe present invention have discovered that the use of a gamma stabilizeris not necessary in order to minimize polyolefin strength loss and odor.As described in the examples, the present invention has been found tominimize strength loss in polypropylene and copolymers without a gammastabilizer. In the case of polyethylene, the present invention hasactually been shown to increase the polyolefin strength. The inventorsof the present invention have also determined that the gamma stabilizeris not needed to reduce the odor associated with the gamma irradiationprocess. Nevertheless, a suitable gamma stabilizer may be incorporatedinto the polyolefin prior to extrusion.

After the polyolefin-based product or fabric to be sterilized has beenobtained, it is normally placed in an oxygen impermeable package. By"oxygen impermeable" it is meant that the material of constructionexhibits a high barrier to oxygen transmission. Those skilled in the artwill recognize such materials as, for example, saran or polyvinylidinechloride. In the case of surgical gowns and other medical fabrics, thegown is generally first placed in a wrap, and the wrapped gown is thenplaced in an oxygen impermeable package. Often, the individual packageis then placed in a larger oxygen impermeable bag, for example a caseliner, with several other individual packages.

Prior to sealing the individual packages containing the polyolefinproduct, an oxygen scavenger is inserted inside the package. The oxygenscavengers of the present invention include commercial grades of iron,such as iron filings, in combination with a catalyst. (See, for example,U.S. Pat. No. 4,992,410, herein incorporated by reference.) Thepreferred oxygen scavenger of the present invention is sold under thetrademark FRESHPAX®, obtained from Multiform Desiccants, Inc., ofBuffalo, N.Y. Other oxygen scavengers that may be used in the presentinvention include copper-based compounds, vitamin C-based compounds, andother like compounds.

The oxygen scavenger should itself be packaged in an oxygen permeablepackage such that the oxygen scavenger is contained within its ownpackage. See for example, U.S. Pat. No. 4,856,650, herein incorporatedby reference. The amount of oxygen scavenger that is needed to removethe oxygen within a sealed package containing a polyolefin product orfabric will of course be dependent upon the volume of oxygen within thatpackage.

Before sealing the package, it is possible to evacuate most of theoxygen from the package. However, this has not been shown to be aseffective as the present invention and vacuum removal of oxygen iseconomically undesirable because of the cost and the increasedproduction time caused by the additional vacuum step. In addition,vacuum packaging causes the final packaged product to be unsightly andthe package is also very difficult to aseptically open. The presentinvention therefore does not require, and is actually designed toeliminate the need for vacuum packaging because a sufficient amount ofoxygen scavenger is supplied to remove the amount of oxygen calculatedto be present within the package. However, as will be apparent to thoseskilled in the art, vacuum packaging may be used in combination with thepresent invention to reduce the amount of scavenger required.

The amount of oxygen scavenger that is inserted into the oxygenimpermeable package is generally ascertained by determining the amountof oxygen scavenger that will remove the amount of oxygen within thepackage prior to sterilization, usually 24 hours or less, to a level of0.01% or 100 parts per million. The manufacturer of the oxygen scavengertypically indicates the amount of oxygen that can be removed in acertain time frame by the particular oxygen scavenger.

Rather than placing the oxygen scavenger within the individual packagecontaining the polyolefin product or gown, the oxygen scavenger may alsobe placed within the larger oxygen impermeable sealable bag thatcontains several of the individually packaged gowns; however, that willnecessitate an oxygen permeable bag for the individual gowns. Anotherembodiment contemplates the incorporation of the oxygen scavenger as apart of the sealable package itself. The oxygen scavenger is thensuitably shielded until the package is ready for use.

In an alternate embodiment, the oxygen scavenger may be contained in, ormounted on, a carrier means such as a cellulosic fiber card. The oxygenscavenger may be incorporated into the card during its manufacture,attached to the card after the card is formed, or the card may be coatedor saturated with an oxygen scavenger-containing solution.

In addition, the package of oxygen scavenger may be affixed to the carditself. An example of the above-described card that may be used todeliver the oxygen scavenger can be found in U.S. Pat. No. 3,843,971,herein incorporated by reference. It should be appreciated, as depictedin U.S. Pat. No. 3,843,971, that the card containing an oxygen scavengermay also be used as a means for its user to aseptically tie thepolyolefin fabric gown.

In another preferred embodiment, an odor mask may be placed inside theindividual polyolefin product or fabric packaging. Unlike the oxygenscavenger, which is believed to bond to free oxygen to prevent theoxygen from combining with the radicals released upon irradiation andwhich cause odors, the mask does not bond with the oxygen. Rather, themask functions to release its own desirable scent such that it competeswith and covers-up any undesirable odors that are not prevented by theoxygen scavenger. The mask can be baby powder-like or any other of thevariety of fragrances that are well-known in the art. An odor maskshould be incorporated into the polyolefin mixture prior to extrusion.

In another embodiment of the present invention, an odor scavenger may beused in conjunction with the previously described oxygen scavenger. Theodor scavenger, such as activated carbon, is normally incorporated intothe individual polyolefin product or fabric packaging by inserting anindividually packaged odor scavenger inside the package containing thepolyolefin product or fabric. It should however be noted that, alone,the odor scavenger will not adequately reduce the odor, and it will notminimize the polyolefin strength loss caused by the irradiation process.Other odor scavengers that may be used include molecular sieves such asthe trademarked product ABSCENTS® (obtainable from U.O.P.), baking sodacompounds, zeolites, and other like compounds.

Once the desired components have been placed within the package, i.e.the polyolefin product or fabric with or without a gamma stabilizerand/or an odor mask, an oxygen scavenger, an odor scavenger, a cardand/or a carrier means, the package is sealed by conventional means andthen sterilized by gamma radiation. Methods for heat sealing oxygenimpermeable packages are well known in the art.

Gamma irradiation techniques are also well-known in the art. For ageneral description of the gamma irradiation of polyolefin fibers seeU.S. Pat. No. 5,041,483, which is herein incorporated by reference.Generally speaking, the amount of radiation necessary to sterilize thepolyolefin product or gown is dependent upon the bioburden of theproduct. Additional factors include the density and configuration of theproduct to be sterilized. A likely range of irradiation is from 1.0 MRADto 10.0 MRAD, more preferably from 1.5 MRAD to 6.0 MRAD.

The materials and methods used in carrying out the present invention maybe more fully understood by reference to the following examples, whichexamples are not intended in any manner to limit the scope of thepresent invention.

EXAMPLE 1

The seven polyolefin-based fabrics listed in Table 1 were gammastabilized with 1% American Cyanamide 2908 type stabilizer. Thesefabrics had no odor mask unless stated otherwise. The test comprised theuse of three 12 square yard samples of each fabric. One sample of eachfabric was kept as a control sample. The other two samples of eachfabric were irradiated at 6 MRADS. One sample of each fabric to beirradiated did not have any oxygen scavenger. The other sample of eachfabric to be irradiated did contain an oxygen scavenger.

                  TABLE I                                                         ______________________________________                                        FABRIC IDENTIFICATION KEY                                                     ______________________________________                                        A.    0.8 oz/yd.sup.2 polyethylene spunbonded not gamma                             stabilized                                                              B.    1.6 oz/yd.sup.2 copolymer SMS not gamma stabilized                      C.    1.8 oz/yd.sup.2 copolymer SMS with gamma stabilizer                     D.    1.8 oz/yd.sup.2 hompolymer SMS with gamma stabilizer                          and an internal odor mask                                               E.    1.8 oz/yd.sup.2 homopolymer SMS with gamma stabilizer                   F.    1.8 oz/yd.sup.2 homopolymer SMS with gamma stabilizer,                        untreated with an alcohol repellant                                     G.    1.6 oz/yd.sup.2 homopolymer SMS not gamma stabilized                    ______________________________________                                         Note:                                                                         The "homopolymer" is 100% polypropylene                                       The "copolymer" is 97% propylene/3% ethylene                             

The oxygen scavenger used was in 2.5"×3" packets, some of which wereable to absorb 400 cc of oxygen, and others capable of absorbing 1,000cc of oxygen. Three 1,000 cc packets were placed in bags containing thesamples for a total of 3000 cc of oxygen absorption capability.

In addition, some of the samples were tested with lower levels of oxygenscavenger. Each of the 12 square yard samples were folded and thenpackaged in 20"×25" nylon/saran/polyethylene high barrier bags from KochSupplies, and then heat sealed. Before heat sealing, as much air aspossible was removed from the bags, however, the bags were not vacuumpacked. The oxygen scavenger used throughout the study was FRESHPAX®from Multiform Dessicants, Inc.

After the samples were irradiated, they were presented to panelists whoevaluated the amount of odor resulting from each sample. The odorpanelists were told to rate the fabrics for odor intensity on a scale of0 to 5, with 0 being no odor at all, and 5 being highly offensive. Ithas previously been determined that an average odor rating of about 1.5or less represents that the product being tested has an acceptable odorrating.

For each sample, the bag was opened and the fabric was spread out in aclosed 10'×12'×9' room. The fabric was allowed to air-out in the roomfor one minute. The odor panelists were then allowed to enter the room,and the door was closed. The panelists then recorded what level, on ascale of 0 to 5, they perceived the odor to be. See Table 2.

                                      TABLE 2                                     __________________________________________________________________________    ODOR RATING AVERAGES                                                          (Sterilized samples dosed at 6 megarads unless otherwise noted)               NO OXYGEN  400 cc OXYGEN                                                                           1200 cc OXYGEN                                                                          3000 cc OXYGEN                                 SCAVENGER  SCAVENGER SCAVENGER SCAVENGER                                      __________________________________________________________________________    A  3.36                        0.94                                           B  3.27                        0.23                                           C  3.85                        1.15                                           D  2.75    2.60      1.28      0.25                                           E  2.63    3.71      1.71      0.00                                           F  4.05                        1.05                                           G  3.08              0.47      1.00                                           __________________________________________________________________________

Once odor panels had been completed on the samples, variations of theamount of oxygen scavenger used were tested on the polyolefin-basedfabrics. The purpose of using different amounts of oxygen scavenger wasto define a lower limit or threshold for the amount of scavenger neededto attain desired strength and odor goals based on the volume of air inthe package. Each of these fabrics was then tested for strength measuredin terms of grab tensile strength (ASTM D-5034), trapezoidal tearstrength (ASTM D-1117), Mullen bursting strength (TAPPI T-403), andElmendorf tear strength (ASTM D-1424). Full strength and odor resultsare represented in Tables 3-10.

                                      TABLE 3                                     __________________________________________________________________________    MD/CD Fabric Grab Tensile Strength                                            (Sterilized samples dosed at 6 megarads unless otherwise                      __________________________________________________________________________    noted)                                                                                                                  POST-     POST-                                        POST-      POST-       STERILIZATION                                                                           STERILIZATION                   PRE-STERILIZATION                                                                          STERILIZATION                                                                            STERILIZATION                                                                             Peak Load-                                                                              Peak Load-                      Peak Load    Peak Load-No. OS                                                                         Peak Load-400 cc OS                                                                       1200 - cc OS                                                                            3000 cc                   __________________________________________________________________________                                                        OS                        A      2.4/3.0      2.4/2.9                          3.6/3.2                  B     17.4/14.7     9.9/7.0                         13.8/14.5                 C     20.6/21.8    12.9/12.1                        19.0/17.2                 D     23.9/21.0    17.1/13.9  16.7/12.5   18.2/18.6 18.7/14.9                 (Trial 1)                                                                     D                  16.7/11.5                        20.9/18.4                 (Trial 2)                                                                     D*                 17.7/17.3              22.3/14.9                           E     24.6/20.4    15.8/13.9  14.2/14.1   18.0/16.2 19.2/16.5                 (Trial 1)                                                                     E                  13.7/12.6                        20.6/17.1                 (Trial 2)                                                                     E*                 18.6/14.9              21.3/17.7                           F     20.8/17.3    13.6/11.7                        18.8/15.4                 G     18.5/18.1    9.9/7.6                12.9/11.9 14.3/12.2                 __________________________________________________________________________                                              POST-     POST-                                        POST-      POST-       STERILIZATION                                                                           STERILIZATION                   PRE-STERILIZATION                                                                          STERILIZATION                                                                            STERILIZATION                                                                             Peak Elong                                                                              Peak Elong.                     Peak Elong   Peak Elong-No. OS                                                                        Peak Elong-400 cc OS                                                                      1200 - cc OS                                                                            3000 cc                   __________________________________________________________________________                                                        OS                        A      90.0%/103.4%                                                                              111.6%/98.2%                     112.8%/111.2%             B     36.8%/44.0%  20.9%/24.0%                      41.6%/27.8%               C     38.7%/43.4%  28.8%/38.6%                      36.8%/49.4%               D     48.3%/42.0%  32.3%/36.9%                                                                              26.7%/32.4% 33.8%/41.3%                                                                             34.1%/36.5%               (Trial 1)                                                                     D                  28.9%/31.2%                      36.9%/39.4%               (Trial 2)                                                                     D*                 33.7%/41.3%            32.2%/37.0%                         E     40.4%/48.9%  28.3%/35.8%                                                                              25.9%/34.5% 29.4%/37.9%                                                                             32.0%/40.1%               (Trial 1)                                                                     E                  24.5%/32.1%                      31.8%/41.7%               (Trial 2)                                                                     E*                 30.6%/38.6%            36.8%/41.7%                         F     46.9%/59.5%  33.4%/41.0%                      39.4%/45.5%               G     37.2%/50.6%  21.7%/22.4%            29.5%/35.0%                                                                             31.4%/35.6%               __________________________________________________________________________     Peak load results are in pounds                                               Peak elongation results are % elongation from 3 inches.                       All results are an average of 5 trials                                        *Dosed at 3 megamds                                                           OS = Oxygen Scavenger                                                    

                                      TABLE 4                                     __________________________________________________________________________    MD/CD Fabric Gmb Tensile Strength Loss                                        (Relative to unsterilized fabric)                                             __________________________________________________________________________                                         POST-                                         POST-     POST-      POST-      STERILIZATION                                 STERILIZATION                                                                           STERILIZATION                                                                            STERILIZATION                                                                            Peak Load-                                    Peak Load-No. OS                                                                        Peak Load-400 cc OS                                                                      Peak Load-1200 cc OS                                                                     3000 cc OS                               __________________________________________________________________________    A    -0%/-3%                         +50%/+6%                                 B    -43%/-52%                       -21%/-1%                                 C    -37%/-44%                        -8%/-21%                                D    -28%/-34% -30%/-40%  -24%/-11%  -22%/-29%                                (Trial 1)                                                                     D    -30%/-45%                       -13%/-12%                                (Trial 2)                                                                     D*   -26%/-18%             -7%/-29%                                           E    -36%/-32% -42%/-30%  -27%-20%   -22%/-19%                                (Trial 1)                                                                     E    -44%/-38%                       -16%/-16%                                (Trial 2)                                                                     E*   -24%/-27%            -13%/-13%                                           F    -35%/-32%                       -10%/-11%                                G    -46%/-58%            -30%/-34%  -23%/-33%                                __________________________________________________________________________                                         POST-                                         POST      POST-      POST-      STERILIZATION                                 STERILIZATION                                                                           STERILIZATION                                                                            STERILIZATION                                                                            Elongation                                    Peak Load-No. OS                                                                        Peak Load-400 cc OS                                                                      Peak Load-1200 cc OS                                                                     3000 cc OS                               __________________________________________________________________________    A    +24%/-5%                        +25%/+8%                                 B    -43%/-45%                       +13%/-36%                                C    -26%/-11%                        -5%/+14%                                D    -33%/-12% -45%/-23%  -30%/-2%   -29%/-13%                                (Trial 1)                                                                     D    -40%/-26%                       -24%/-6%                                 (Trial 2)                                                                     D*   -30%/-2%             -33%/-12%                                           E    -30%/-27% -36%/-29%  -27%/-23%  -21%/-18%                                (Trial 1)                                                                     E    -39%/-34%                       -21%/-15%                                (Trial 2)                                                                     E*   -24%/-21%             -9%/-15%                                           F    -29%/-31%                       -16%/-24%                                G    -42%/-56%            -21%/-31%  -16%/-30%                                __________________________________________________________________________     *Dosed at 3 megarads                                                     

                                      TABLE 5                                     __________________________________________________________________________    MD/CD Fabric Trapezoidal Tear Strentgth                                       (Sterilized samples dosed at 6 megarads unless otherwise                      __________________________________________________________________________    noted)                                                                                                                  POST-     POST-                                        POST-      POST-       STERILIZATION                                                                           STERILIZATION                   PRE-STERILIZATION                                                                          STERILIZATION                                                                            STERILIZATION                                                                             Tear Mean-                                                                              Tear Mean-                      Tear Mean    Tear Mean-No. OS                                                                         Tear Mean-400 cc OS                                                                       1200 cc OS                                                                              3000 cc                   __________________________________________________________________________                                                        OS                        A     1.82/1.09    1.23/0.98                        1.48/1.21                 B     3.06/2.75    0.86/0.64                        1.96/2.10                 C     4.58/4.35    2.07/1.78                        3.89/3.12                 D     3.77/4.78    1.86/1.57  2.11/2.00   3.40/2.81 2.96/2.37                 (Trial 1)                                                                     D                  2.08/1.60                        3.36/3.64                 (Trial 2)                                                                     D*                 2.60/2.78              3.64/3.31                           E     3.93/3.18    1.86/1.70  1.86/1.55   2.66/2.50 2.78/2.24                 (Trial 1)                                                                     E                  1.88/1.91                        3.55/2.73                 (Trial 2)                                                                     E*                 2.94/2.09              3.24/3.05                           F     4.30/3.58    2.02/2.03                        2.95/2.57                 G     3.66/3.15    1.30/0.93              2.64/3.18 1.64/1.51                 __________________________________________________________________________                                  POST-       POST-     POST-                                        POST-      STERILIZATION                                                                             STERILIZATION                                                                           STERILIZATION                   PRE-STERILIZATION                                                                          STERILIZATION                                                                            Avg.1st + high                                                                            Ave.1st + high                                                                          Avg.1st + high-                 Avg. 1st + high                                                                            Avg. 1st + high No OS                                                                    -400 cc OS  1200 cc OS                                                                              3000 cc                   __________________________________________________________________________                                                        OS                        A     4.07/2.11    2.47/1.82                        3.96/2.29                 B     6.55/5.74    2.17/1.48                        4.15/4.53                 C     9.14/8.78    4.37/3.58                        8.31/5.91                 D      8.03/10.49  4.30/3.46  4.00/3.64   6.22/5.12 6.63/5.05                 (Trial 1)                                                                     D                  4.88/3.96                        6.47/7.17                 (Trial 2)                                                                     D*                 5.14/5.86              6.47/6.60                           E     8.51/7.33    4.11/3.60  3.53/3.10   4.97/4.71 5.94/4.80                 (Trial 1)                                                                     E                  3.89/4.04                        6.44/5.17                 (Trial 2)                                                                     E*                 6.04/4.14              6.15/5.49                           F     9.12/7.34    4.64/4.48                        6.30/5.73                 G     6.88/5.96    3.04/2.15              5.42/4.34 3.72/3.51                 __________________________________________________________________________     All results are in pounds                                                     All results are an average of 5 trials                                        *Dosed at 3 megamds                                                      

                                      TABLE 6                                     __________________________________________________________________________    MD/CD Trapezoidal Tear Strength Loss                                          (Relative to unsterilized fabric)                                             __________________________________________________________________________                                             POST-                                      POST-       POST       POST        STERILIZATION                              STERILIZATION                                                                             STERILIZATION                                                                            STERILIZATION                                                                             Tear Mean                                  Tear Mean-No. OS                                                                          Tear Mean-400 cc OS                                                                      Tear Mean-1200 cc OS                                                                      3000 cc OS                           __________________________________________________________________________    A     -32%/-10%                          -19%/+11%                            B     -72%/-77%                          -36%/-24%                            C     -55%/-59%                          -15%/-28%                            D     -51%/-62%   -44%/-58%  -10%/-41%   -22%/-50%                            (Trial 1)                                                                     D     -45%/-67%                          -11%/-24%                            (Trial 2)                                                                     D*    -31%/-42%              -32%/-21%                                        E (Trial 1)                                                                         -53%/-47%   -53%/-51%  -59%/-58%   -29%/-30%                            E (Trial 2)                                                                         -52%/-40%                          -10%/-14%                            E*    -25%/-34%              -42%/-36%                                        F     -53%/-43%                          -31%/-28%                            G     -65%/-71%              -28%/+1%    -55%/-52%                            __________________________________________________________________________                      POST-      POST-       POST-                                      POST-       STERILIZATION                                                                            STERILIZATION                                                                             STERILIZATION                              STERILIZATION                                                                             Avg. 1st + high                                                                          Avg. 1st + high                                                                           Avg.1st + high                             Avg. 1st + high No OS                                                                     -400 cc OS 1200 cc OS  3000 cc OS                           __________________________________________________________________________    A     -39%/-14%                           -3%/+9%                             B     -67%/-74%                          -37%/-21%                            C     -52%/-59%                           -9%/-33%                            D     -47%/-67%   -50%/-65%  -23%/-51%   -17%/-52%                            (Trial 1)                                                                     D     -39%/-62%                          -19%/-32%                            (Trial 2)                                                                     D*    -36%/-44%              -19%/-37%                                        E (Trial 1)                                                                         -52%/-51%   -59%/-58%  -42%/-36%   -30%/-35%                            E (Trial 2)                                                                         -54%/-45%                          -24%/-29%                            E*    -29%/-44%              -28%/-25%                                        F     -49%/-39%                          -31%/-22%                            G     -56%/-64%              -21%/-27%   -46%/-41%                            __________________________________________________________________________     *Dosed at 3 megarads                                                     

                                      TABLE 7                                     __________________________________________________________________________    MD/CD Fabric Elmendorf Tear Strentgth                                         (Sterilized samples dosed at 6 megarads)                                                         POST-      POST-       POST-     POST-                                        STERILIZATION                                                                            STERILIZATION                                                                             STERILIZATION                                                                           STERILIZATION             PRE-STERILIZATION  No OS      400 cc OS   1200 cc OS                                                                              3000 cc                   __________________________________________________________________________                                                        OS                        B     640/551      244/212                          352/388                   C     816/812      408/352                          616/494                   D     780/736      412/404    390/384     525/403   500/448                   (Trial 1)                                                                     D                  348/332                          460/404                   (Trial 2)                                                                     E     736/752      308/292    378/371     410/442   508/388                   (Trial 1)                                                                     E                  364/344                          448/436                   (Trial 2)                                                                     F     717/586      288/276                512/416                             G     744/755      346/364                442/467                             __________________________________________________________________________     All results are in grams                                                      Results are an average of 5 trials for some, 8 trials for others         

                                      TABLE 8                                     __________________________________________________________________________    Fabric Mullen Burst Strength                                                  (Sterilized samples dosed at 6 megarads)                                                         POST-      POST-       POST-     POST-                                        STERILIZATION                                                                            STERILIZATION                                                                             STERILIZATION                                                                           STERILIZATION             PRE-STERILIZATION  No OS      400 cc OS   1200 cc OS                                                                              3000 cc                   __________________________________________________________________________                                                        OS                        B     24.4         10.7                             24.4                      C     32.0         20.6                             29.6                      D     33.9         23.9       22.8        28.5      26.5                      (Trial 1)                                                                     D                  23.8                             27.8                      (Trial 2)                                                                     E     31.3         20.3       21.0        26.5      28.5                      (Trial 1)                                                                     E                  20.7                             29.8                      (Trial 2)                                                                     F     28.4         20.9                             29.5                      G     34.9         20.5                             25.6                      __________________________________________________________________________     All results are in lbs/sq. inch                                               Results are an average of 12 trials, except group G (5 trials)           

                                      TABLE 9                                     __________________________________________________________________________    MD/CD Elmdorf Tear Strength Loss                                              (relative to unsterilized fabric)                                             POST-          POST-     POST-     POST-                                      STERILIZATION  STERILIZATION                                                                           STERILIZATION                                                                           STERILIZATION                              No OS          400 cc OS 1200 cc OS                                                                              3000 cc OS                                 __________________________________________________________________________    B    -62%/-62%                     -45%/-30%                                  C    -50%/-57%                     -25%/-40%                                  D    -47%/-45% -50%/-48% -33%/-45% -36%/-39%                                  (Trial 1)                                                                     D    -55%/-55%                     -41%/-45%                                  (Trial 2)                                                                     E    -58%/-61% -49%/-51% -44%/-41% -35%/-47%                                  (Trial 1)                                                                     E    -51%/-54%                     -39%/-42%                                  (Trial 2)                                                                     F    -60%/-53%                     -30%/-29%                                  G    -54%/-52%                     -41%/-48%                                  __________________________________________________________________________

                                      TABLE 10                                    __________________________________________________________________________    Mullen Burst Strength Loss                                                    (relative to unsterilized fabric)                                             POST-          POST-     POST-     POST-                                      STERILIZATION  STERILIZATION                                                                           STERILIZATION                                                                           STERILIZATION                              No OS          400 cc OS 1200 cc OS                                                                              3000 cc OS                                 __________________________________________________________________________    B    -56%                          -0%                                        C    -36%                          -8%                                        D    -30%      -33%      -16%      -22%                                       (Trial 1)                                                                     D    -30%                          -18%                                       (Trial 2)                                                                     E    -35%      -33%      -15%      -9%                                        (Trial 1)                                                                     E    -34%                          -5%                                        (Trial 2)                                                                     F    -26%                          +4%                                        G    -41%                          -27%                                       __________________________________________________________________________

It is important to note that the bulk of the fabrics used in this studywere sterilized at 6 MRADS. Typically, polyolefin containing surgicalgowns used in hospitals are sterilized at between 2 and 2.25 MRADS.However, some polyolefin-based surgical products are sterilized at 6MRADS. Because increased MRADS cause decreased polyolefin strength andpotentially increased levels of odors, the 6 MRAD radiation dosage usedin this study had the potential to cause both an increase in the levelof odors, and an increase in strength loss caused by normal radiation.However, the tests demonstrate that even under these extreme conditionsthe invention functions to decrease both odors and strength loss.

A. ODOR RESULTS

The samples that contained oxygen scavenger received significantly lowerodor ratings than samples without oxygen scavenger in all the odorpanels. See Table 2. The panelists rated the fabrics without an oxygenscavenger as highly offensive, with an average odor rating of nearly 3.5on a 5 point scale. When 3000 cc of oxygen scavenger were used, theaverage odor rating was below 1.0. As previously indicated, an averageodor rating below 1.5 is acceptable. Therefore, an average rating ofbelow 1.0 is indicative of very favorable results. Every fabric testedusing an oxygen scavenger was rated as having a significantly lower odorrating than the same fabrics without the oxygen scavenger.

In the odor panels, it was found that the homopolymer with odor mask didnot perform better than homopolymer without odor mask. See Table 2. Bothfabrics had nearly the same odor ratings at all oxygen scavenger levels,including one with no oxygen scavenger.

Another interesting finding was that the use of activated carbon as anodor scavenger in conjunction with the oxygen scavenger did notsignificantly reduce odor. Two samples were used with activated carbonand 400 cc of oxygen scavenger. Neither of these samples was rated lowerin the odor panels than 400 cc of oxygen scavenger alone. See Table 2,columns D and E.

Although the use of 3000 cc of oxygen scavenger proved to be veryeffective in reducing odor, the cost of using this much FRESHPAX®scavenger is relatively high. It was therefore necessary to attempt tofind a lower amount of scavenger that would perform as effectively as3000 cc of scavenger. It was found that 1200 cc of oxygen scavengerperformed nearly as well as 3000 cc of oxygen scavenger in the samepreviously defined bags. See Table 2. The odor ratings given by thepanelists were in the 1 to 2 range for fabrics with 1200 cc of oxygenscavenger. A different panel was used for these tests and it will berecognized that some variation may be expected due to the experiencelevel of the individual panelists. In this case, it is thereforebelieved that the actual odor ratings for the fabrics with 1200 cc ofoxygen scavenger with a panel equivalent to the previous one may beactually below 1.0.

In an effort to ascertain the minimum amount of scavenger that wouldyield acceptable odor levels, some of the fabrics were also tested with400 cc of oxygen scavenger. The panelists rated these fabrics as beingquite high. Thus, it is believed that the minimum amount of oxygenscavenger needed to reduce the odors to an acceptable level is greaterthan 400 cc of oxygen scavenger for the test package used. See Table 2.

One particularly encouraging result of the odor panels was theperformance of unstabilized materials when used with oxygen scavenger.Previously it was believed that polyolefin fabrics needed to be gammastabilized during fabric formation in order to prevent the high ratingof post-gamma irradiation odor. However, when 3000 cc of oxygenscavenger was used, both the unstabilized homopolymer and the stabilizedcopolymer received odor ratings around 1.0. The unstabilized homopolymeralso received an odor rating below 1.0 when used with only 1200 cc ofoxygen scavenger. See Table 2. These results of the unstabilizedmaterials are important due to the cost-effectiveness of not having touse a gamma-stabilizer, which, in turn, significantly reduces the costof producing the polyolefin-based fabrics.

B. STRENGTH RESULTS

In addition to the odor tests, various strength tests were performed onthe gamma irradiated fabrics. Quite a few interesting discoveries weremade in the strength evaluation. The most interesting discovery was ofthe effect the oxygen scavenger had on the strength of spunbondedpolyethylene. There was no difference in the strength of theunsterilized sample of polyethylene and the sample that was radiatedwithout oxygen scavenger. However, when polyethylene was sterilized and3000 cc of oxygen scavenger was used, there was a strength gain ofnearly 40% over the polyethylene prior to its irradiation. (MD=machinedirection; CD=cross direction)

    ______________________________________                                                                         3000 cc O.sub.2                              Fabric   Pre-sterilized                                                                           No O.sub.2 Scavenger                                                                       Scavenger                                    ______________________________________                                        Potyethytene                                                                           2.4 MD/3.0 2.4 MD/2.9 CD                                                                              3.6 MD/3.2 CD                                         CD                                                                   ______________________________________                                    

Another notable result from the strength testing was that there was nosignificant strength difference between a homopolymer with an odor maskand a homopolymer without an odor mask. See Tables 3-10. Given that anodor mask did not provide significant advantages in preventing odor, itis not believed to be a component that is absolutely necessary toachieve acceptable results. Both polypropylene homopolymers fabrics lostabout 40% of their pre-sterilized strength when no oxygen scavenger wasused. When 3000 cc of oxygen scavenger were used, this strength loss wasreduced to about 20%. The strength loss was also only about 20% when1200 cc of oxygen scavenger were used. In comparing strength and odorqualities, 1200 cc of scavenger appeared to perform as well as 3000 ccof scavenger. When these fabrics were tested with only 400 cc ofscavenger, strength losses were in the 30%-40% range.

    __________________________________________________________________________                                         1200 cc O.sub.2                                                                        3000 cc O.sub.2                 Fabric  Pre-sterilized                                                                         No O.sub.2 Scavenger                                                                   400 CC O.sub.2 Scavenger                                                                 Scavenger                                                                              Scavenger                       __________________________________________________________________________    Homopolymer                                                                           23.9 MD/21.0 CD                                                                        17.1 MD/13.9 CD                                                                        16.7 MD/12.5 CD                                                                          18.2 MD/18.6 CD                                                                        18.7 MD/14.9 CD                 w/odor mask                                                                   Homopolymer                                                                           24.6 MD/20.4 CD                                                                        15.8 MD/13.9 CD                                                                        14.2 MD/14.1 CD                                                                          18.0 MD/16.2 CD                                                                        19.2 MD/16.5                    __________________________________________________________________________                                                  CD                          

It therefore appears that greater than 400 cc of oxygen scavenger mustbe used to reduce post-irradiation strength loss such that the productstrength is within an acceptable range.

In comparing the strength of the homopolymer and the copolymer,non-sterilized homopolymer was generally about 20% stronger than thenon-sterilized copolymer. However, the post-sterilization strengthlosses were greater in the homopolymer than the copolymer. Because thecopolymer did not lose as much strength, the strength of the homopolymerand copolymer was about the same when both irradiated fabrics werepackaged with 3000 cc of scavenger.

    __________________________________________________________________________    Fabric   Pre-sterilized                                                                         No O.sub.2 Scavenger                                                                    3000 cc O.sub.2 Scavenger                         __________________________________________________________________________    Homopolymer                                                                            24.6 MD/20.4 CD                                                                        15.8 MD/13.9 CD                                                                         19.2 MD/16.5 CD                                   Copolymer                                                                              20.6 MD/21.8 CD                                                                        12.9 MD/12.1 CD                                                                         19.0 MD/17.2 CD                                   __________________________________________________________________________

The unstabilized fabrics were not as strong as their corresponding gammastabilized fabrics. Taking into account their basis weights (that is, ifthe unstabilized materials had been 1.8 ounce per square yard), theunstabilized fabrics were approximately 15% weaker than the stabilizedfabrics. When sterilized without oxygen scavenger, both the unstabilizedhomopolymer and unstabilized copolymer lost nearly 50% of their initialstrength. The use of 3000 cc of oxygen scavenger reduced the strengthloss in the unstabilized materials. The unstabilized copolymer strengthloss was reduced to about 20% with 3000 cc of oxygen scavenger. However,the strength loss for both 1200 cc and 3000 cc of oxygen scavenger inthe unstabilized homopolymer was still nearly 30%. At a 1.6 ounce peryard basis weight of fabric and 1200 cc of oxygen scavenger, thestrength of the unstabilized materials was well below that of thecorresponding stabilized materials. Where strength losses approach orexceed 50% of the pre-irradiated product, the commercial value of theproduct is considerably reduced.

    __________________________________________________________________________    Fabric                                                                        Scavenger                                                                              Pre-sterilized                                                                         No O.sub.2 Scavenger                                                                    3000 cc O.sub.2                                   __________________________________________________________________________    Unstabilized                                                                           17.4 MD/14.7 CD                                                                        9.9 MD/7.0 CD                                                                           13.8 MD/14.5 CD                                   homopolymer                                                                   Unstabilized                                                                           18.5 MD/18.1 CD                                                                        9.9 MD/7.6 CD                                                                           14.3 MD/12.2 CD                                   copolymer                                                                     __________________________________________________________________________

Two samples that performed well in both strength and odor were thehomopolymer and homopolymer with odor mask dosed at 3 MRADS. Whensterilized without oxygen scavenger, the strength loss in thehomopolymer fabrics was approximately 25%, which was significantly lessthan the strength loss associated with 6 MRADS. The homopolymer fabricsirradiated with 3 MRADS lost only 15% of their strength when sterilizedin the presence of 1200 cc of oxygen scavenger. In addition, the 3 MRADfabrics had nearly negligible odor with oxygen scavenger.

    ______________________________________                                        Fabric     No O.sub.2 Scavenger                                                                        1200 cc O.sub.2 Scavenger                            ______________________________________                                        Homopotymer                                                                              17.7 MD/17.3 CD                                                                             22.3 MD/14.9 CD                                      w/odor mask                                                                   Homopolymer                                                                              18.6 MD/14.9 CD                                                                             21.3 MD/17.7 CD                                      ______________________________________                                    

Turning to the Figure, a bag 10 is illustrated which may be used, forexample, for packaging individual surgical products, such as gowns,drapes and packs. As shown, bag 10 comprises outer barrier layers 12, 14which are gas impermeable and sealed, for example, by means of heat seallines 16, 18, and 20. An internal pouch 22 is formed by gas permeablelayer 24 which may be sealed to both gas impermeable layers along lines16 and 18 by means of the same heat seals but is sealed only to oneimpermeable layer, such as 12, along line 28 so that the pouch contents,scavenger 26, is exposed to the gas inside bag 10. In use, the product29 to be sterilized is loaded through product loading end 30 after seallines 16, 18, 20 and 28 have been formed. At about the same time,scavenger 26 is loaded into pouch 22, and a final seal line may then beformed closing product loading end 30. The pouch contents arenon-obvious to the ultimate user yet have full access to the product tobe sterilized. If desired, notches 34 may be cut in product removal endedges to facilitate product removal.

Thus, while methods for reducing odors and strength loss caused by theirradiation of polyolefin-based products, carrier means to effect same,the products of the methods, and modifications thereof have been shownand described in detail herein, various additional changes andmodifications may be made without departing from the scope of thepresent invention.

We claim:
 1. A method for reducing the undesirable side effectsassociated with the irradiation of a polyolefin-based product comprisingthe step of exposing said polyolefin-based product to an oxygenscavenger, both of which are in or a part of a sealed container prior tosaid irradiation.
 2. A method for reducing odors associated with thesterilization by irradiation of polyolefin-based products comprising thesteps of:a) inserting a polyolefin-based product into an oxygenimpermeable sealable bag; b) inserting an oxygen scavenger into saidbag; c) sealing said bag to prevent air from either entering or escapingsaid bag; and d) sterilizing said sealed bag and its contents with gammaradiation.
 3. The method of claim 2, wherein said polyolefin-basedproduct includes an odor mask.
 4. The method of claim 2, wherein saidmethod further comprises evacuating substantially all of the air fromsaid bag prior to sealing said bag.
 5. The method of claim 2, whereinsaid polyolefin-based product is a homopolymer.
 6. The method of claim2, wherein said polyolefin-based product is a copolymer.
 7. The methodof claim 2, wherein said polyolefin-based product comprises a fabric. 8.The method of claim 2, wherein said polyolefin-based product furthercomprises a gamma stabilizer.
 9. The method of claim 2, wherein saidmethod further comprises inserting an odor scavenger into said bag priorto sealing said bag.
 10. The method of claim 2, wherein said oxygenscavenger is contained in a carrier means.
 11. The method of claim 2,wherein said oxygen scavenger is connected to a carrier means.
 12. Apolyolefin-based product that has been sterilized according to themethod of claim
 2. 13. A method for reducing strength loss associatedwith the sterilization of a polyolefin-based product that has apre-sterilization strength comprising the steps of:a) inserting apolyolefin-based product into an oxygen impermeable sealable bag; b)inserting an oxygen scavenger into said bag; c) sealing said bag toprevent air from either entering or escaping said bag; and d)sterilizing said sealed bag and its contents with gamma radiation. 14.The method of claim 13, wherein said method further comprises evacuatingas much air as possible from said bag prior to sealing said bag.
 15. Themethod of claim 13, wherein said polyolefin-based product is ahomopolymer.
 16. The method of claim 13, wherein said polyolefin-basedproduct is a copolymer.
 17. The method of claim 13, wherein saidpolyolefin-based product comprises a fabric.
 18. The method of claim 13,wherein said polyolefin-based product further comprises a gammastabilizer.
 19. The method of claim 13, wherein said method furthercomprises inserting an odor scavenger into said bag prior to sealingsaid bag.
 20. The method of claim 13, wherein said oxygen scavenger iscontained in a carrier means.
 21. The method of claim 13, wherein saidoxygen scavenger is connected to a carrier means.
 22. A polyolefin-basedproduct that has been sterilized according to the method of claim 13.23. A method for increasing the strength of a polyethylene-based productcomprising:a) exposing said polyethylene-based product to an oxygenscavenger, both of which are contained in an oxygen impermeable package;and b) gamma-irradiating said package and said product such that thestrength of said product is greater than the prior-to-irradiationstrength thereof.
 24. A polyethylene-based product that has beensterilized according to the method of claim
 23. 25. A method forpreventing the formation of oxygenated compounds that are formed after apolyolefinic product is exposed to gamma radiation in the presence ofoxygen comprising the steps of placing said polyolefinic product and anoxygen scavenger in a sealed container and irradiating said product andcontainer with gamma radiation at a level of exposure sufficient tosterilize said product.